Question about stack API

I’m working on integrating Rancher with Terraform and I’ve got 1 last item to implement: stack upgrades.
It seems that the docker_compose and rancher_compose fields for a stack (or environment in v1) get populated with the raw, un-interpolated contents from a catalog entry when creating a stack from a catalog entry, but when you upgrade the stack to a newer version of the catalog entry, those values are not changed.

When calling the API to do a stack upgrade and passing an explicit docker_compose and rancher_compose, the values are not updated either, yet somehow the exportConfig action on the stack, returns the correct, interpolated file contents.
This is making it difficult to detect modifications to these resources from Terraform’s perspective and I’m just wondering if I’m missing something here.